Detonating explosive charge and method of impressing surfaces employing same



y 9 J. H. COOK 2,604,042

DETONATING EXPLOSIVE CHARGE AND METHOD OF IMPRESSING SURFACES EMPLOYINGSAME Filed July 30, 1948 3 Sheets-Sheet l II I I I/ l/II Attorneys y 9 2J. H. cook 2,604,042.

TING LOSIVE CHARGE ETHOD DET OF BESS SURFACES EIIPL SAME Filed July 30.1948 3 Sheets-Sheet 3 INVENTOR JOHN. HENRY COOK svzwawf $404M) ATTORNEYSPatented July 22, 1952 nairomrmo nxrtosivg cnaiges METHOD OFI'IltflRESSING .EMPI'JOYING SAME John .:Henry tGook Ayrshire,scotlandfassiginor" :to ImDerialUlremical Industries Limited, .a cor-:poration of Great Britain 7 Application'ZIuly 30, 194-8, Serial"No.'4160'5 In Great Britain October 6, 1947 .9-Claims. (01. 101-4012)"The-present invention is concerned with-a new and improved l metho-d ofexplosively impressing markings in"low-irelief into=a metal opiatewhereby impressed metal: plates suitable i fo risuchipurp'oses ase'mbossing or printingsheet=:materials:may:be "obtained. Theinventionfurtherrelates to asn'ew 'form of explosive charge suitableio'r impressing in' l'ow relief on a m'etal'platemarkings simulatingthose provided by the -boundaries between sur- "faces of 1 differingrelief in a item-plate interposed betweenit and the metal plate.

It as :a'n object of the invention t'o provide a pr'actic'alilemethodfor the productionrof metal plates-"of at least several'square inches inarea impressed with designso'r other markings in low relief suitable forembossing, printing orthe like --in a more expeditious inanner than bythe usual -r'neth'ods. It is also an ob'ject of the invention -to"provide a new "or improved form of explosive charge having *a plane endof --subs'tantial area characterised "in that when its detonation isiniti'ated from its opposite end the detonation wave "front-at'saidplane'endfis substantially free from curvature Y Other Objects of theinvention will appear hereinafter. i I It has-long been known that i byplacing a coin -qn--a-=meta1 p1ate and initiating "detonation of anexplosive charge superposed -on "the coin, the "design on 'the face ofthe coin presented to the metal 'plate 'can'bemoi'e "or less faithfullyreproduced on the plate in reverse that- 1s to say the hollow portionsof the design on the coin will i'appeara's raised portions inithe plate,and the relief portions of the d si n 'on the coin will be indentedinfthe plate; on -the other hand the sha e and markings of a .leaf, apiece of lace, or'llke flat object "of :small "area "made 'of softjiie'structiblemateiial laid on a metal plate have been shownmarked on ametal plate in positive image by detonating a plane=ended explosivecartridge superposed on "the object. Hitherto however the .so .impressedplates have been regarded merely as scientific curiosities and no.jinilustrial applicationhas'been made of'thepossilbilities T01impressing ,metal [plates with designs "by means oftexplosives.

Wh'enfia comparatively short cylinder or other plane fended columnarbody of "detonating explosive having an axis perpendicular to its endsand thesame crosssection throughout its axial length hasfits-.detonation initiated ,from a ,point at one ,endof itsakis, thedetonation wave front advancing through the column .is convex. Owing tothis ,convexitypf the detonation wave. front, no design "-2 v impressedby-means'of anexplosivecolumn, whose detonation is initiated-by-a-detonator;-at its remote end, on azmetalgplatesfrom an;inter.posedtemplate or :stencil cut with a design in low relief can thesatisfactorily simulated, except in a :small area immediately around:the :;axis of the column ;,so that unless the cross'sectional area-ofaherexplosive :column andthe v design as 'a whole;;is .small :therendering :of the :design becomes moreaand 'rmore fn'oticeablyindistinct as the ;periphery of the cclisc is approacheiwith the resultsthat the impressed metal plate obtained is vof inolpr-actical value.

This imperfection 10f impression "presents a problem IO which apractical solution is not easily found. 'fihusamultiple initiation bymeans of detonators spaced at ;intervals over the area of :the remotetend cof the :explosive column :does not usually effect the desiredresult, since the "resulting designr'on the metalaplate may-beimarrjedby blemishes repres'enting the .lines :where the convex detonation wavefront surfaces intersect.

tirhile l the replacement zofia portion of, the length or the -column ofexplosive aby a tliscxofI-an explosive of highervlocity of..'dtonation-than Ethat "plane -base-is uriintertupted by any recess forspro- -jection,-said conical forni being-if :desiredftnuhcated by one'or more surfaces passing perpen- -dicula'rly through its base, and indeton'ation inducing relationship with said-explosive :charge, acovering of =a thickness of an explosive ofia higher Velocity ofdetonation extending over the whole of its-conical curved surface, thede'tonati'on initiating ineans bing -at the apes; the sine of the baseangle of the cone being equal t'o the -quotientofthe-velocity-ofdetonation-'o'f-theeizplosive of relatively lower"velocity amuse rbyoffthe'exp'losive of relatively higher velocity;

The detonation wave front transmitted to'and beyond the base of such "anexplosive-charge is a plane parallel fto said 'base. The longer timethan would be otherwise required for an nn iil'se tob'etransmitted'fiornthe"apical regiontv folly or, partly ialong the sloping length of thethickness of explosive'of higher velocityoif deton ti'o'n covering thecore explosive than directly-along the axis to: the"'coneiis compensafmufor "bythe v reduced thickness ioffthefexplosive offlcwer velocity ofdetonation through which the impulse must be transmitted before it canreach the base, so that at every point of the base of the cone, whetheror not this is truncated as aforesaid, there arrivesan impulse at thesame instant of time.

In the method of explosively impressing low relief markings in a metalplate according to the present invention, the apically disposedinitiating means detonates the composite explosive charge with aresultant plane detonation wave front. Between the base of the explosivecharge and the metal plate there is'interposed a sheet of destructiblecompressible material having predetermined local variations in itsthickness or in the nature of the material composing it. The aforesaiddestructible compressible material causes absorption of the energy ofdetonation directed through it in correspondingly differing degrees atthe respective parts of its area. If desired, further cushioning sheetmaterial of uniform absorption capacity over its area may be employed toabsorb the energy to an additional degree. The higher energy absorbingportions of the sheet of destructible compressible material cause themetal plate portions beneath them to be subjected to less energy ofdetonation than those portions of the metal plate underlying the lesserenergy absorbing portions of the destructible sheet material. As

a result of this, as is explained more fully hereinafter, variousdesigns may be impressed in the metal surfaces.

The aforesaid composite explosive charge preferably includes also as anelement intern posed between said first mentioned element and the sheetof destructible compressible material a parallel plane-ended column ofuniform cross section, having its columnar axis perpendicular to itsplane ends, of an explosive composition whose detonation is initiatedfrom one of its plane ends through the base of said first mentionedelement, whereof the core explosive has a velocity of detonation notexceeding and preferably lower than that of the explosive of saidparallel plane-ended column. By the method of the present inventiondesigns extending over areas ranging up to some hundreds of squareinches may be satisfactorily impressed.

The invention will be further understood by reference to thediagrammatic drawings accompanying the provisional specification,whereof Figure l is a vertical axial section and Figure 2 is a top planview of an assembly for executing a design on a metal plate according toone form of the invention, Figure 3 is a plan view of a sheet ofdestructible compressible material bearing an ornamental design formingpart of the aforesaid assembly, Figure 4 is aplan view of the metalplate having the ornamental design inlow relief obtained as a result ofthe detonation, Figure 5 is a vertical axial section of a modificationof Figure 1, and Figure 6 is a top plan view of the modification ofFigure 5.

In Figure 1, I is a steel anvil, 9 is a sheet of cushioning materialsuch as cardboard, 8 is a brass plate, 6 is the smooth cardboard baseand 3 the cardboard wall of a container. I, seen also in Figure 3, is asheet of hard cardboard cut in stencil with the ornamental design shownin Figure 3. A and-'1 are thin partitions of stiff paper or the like. isa' cylindrical charge of an explosive of a velocity of detonation about600 metres, per second and 5 is a conical charge of an explosiveofvelocity of detonation about 2300 metres per second capable'of inducingthe was detonation of the explosive 5 when it is itself detonated by acharge 5 of a velocity of detonation abotu 5800 metres per secondconstituing a layer of uniform thickness covering the coni= cal chargeand capable of detonating the latter through the intervening thin sheet4 i The base angle of the cone is 23 22. I I is a tetryl primer and I2is an electric detonator.

When the electric detonator I2 is fired the primer II is detonated andthe latter radially initiates the detonation of the explosive charge 5,which in turn initiates the detonation of the explosive charge 5 acrossthe intervening sheet '4 The thickness of the explosive 5 of lowervelocity of detonation than that of explosive 5 that has to be traversedbefore the detonation impulse meets the explosive 5 is greatestvertically below the apex of the cone, and the angle of the cone is suchthat the detonation impulse that has travelled down the outer layerexplosive of higher velocity 5 arrives at the circumference of its baseat precisely the same instant as that travelling axially arrives at thecenter of its base. At this instant a detonation impulse arrives atevery point at the interface between the explosive 5 and 5 so that thedetonation wave front at this interface is not convex but plane. Hencethe detonation induced in the cylindrical explosive charge 5 travelsthrough it with a plane wave front and everywhere on the sheet I thedetonation impinges normal to its surface. The upstanding parts of thedesign on the sheet I however, absorb more of the energy of thedetonation than the blank portions, so that the metal plate 8 is moredeeply impressed beneath the blank portions than beneath the upstandingportions. The base 6 of the container absorbs some of the detonationenergy before it reaches the sheet I. The cushioning sheet 9 helps toprevent the plate 8 from being bent or broken. It is a remarkable fact,however, that the design rendered on the plate 8 is as a whole somewhatlarger. than that on the said sheet I, as is shown in Figures 3 and 4.The design is distinctly rendered on the plate over the whole area ofthe design. I

The greater the difference between the velocities of detonation of thecore explosive and of the outer explosive in the conical portion of thecharge, the flatter may be the shape of the cone and hence the less theamount of explosive material required to produce a plane detonation wavefront. It may therefore be preferable to employ as the core explosiveone that would have a substantially lower velocity of detonation than isusually desirable for impressing the markings effectively on a metalplate-so long as it' is capable of initiating the detonation of theparallel plane-ended column of 'theexplosive of velocity of detonationsuitable for impressing the markings. Thus the core explosive in theconical portion of the charge may advantageously have a velocity ofdetonation for instance of about 2,000-2500 metres per second and thatof the explosive of the parallel plane-ended column may range up toabout 3300-3800 metres per second or more depending on the depth ofimpression required, and the nature of the material of the metal plateand the extent to which the explosive charge is cushioned. I

The velocity of detonation of the, explosive on the conically curvedsurface should theoretically be as high as possible but economicalrangers doesfi-not-hecessarily follow that *the depth of theimpressionsall-overthe surface workedupon will be identical, since thetwo explosives presinthe conical 'portion-may differ markedly in jpoweror density so that the-energy transmitteii from the base of thisgconical --structure will not-in::general"'be the same in amount aiwallparts of its surface. This differential effect, however, is minimisedwhen the conical portion is somewhat truncated by one "or more surfacesnormal to itsf'base, andyalso when this 'portion is "employed 'as theinitiating "means .in conjunctionflwith a parallel plane-endedcylindrical column of explosive in the "aforesaid manner,especially'when the'explosive used =for-thecore of the ,conicaliporti-onisofa' substanti-ally -low'ervelocity of detonationthan that-of theexplosive in said column and the velocity ofdetonation 'of the explosiveon the -conically curved surface is substantially higher than that ofthe explosive in .said ,parallel plane-ended column.

Tn 'the 'case where a circular area is to be worked upon, the peripheryo'f the -base of the cone may ibercomplete although jitjis iusuallydesirable, that the form. of the charge, or portion .of theldhargeshould be truncatedso that. at;least that portion of the cone lyingoutside .the truncated surface perpendicular .to the ;base' 'of the,complete cone and intersecting it .at .the

junction between the two explosives comprising the cone should beomitted, and it'is sometimes preferable that the truncation should besuch asrto omit an annular-portion of the complete cone -lying outside acylindrical surface perpendicular to and intersecting the base somewhatnearerthe-axis-ofthe cone; In the case where a non-:circular arealis :to;be worked amen, it will in generallbe.gadvisablesthatthe truncation ofthe cone should be such as to omit those portions of the complete conethat lie outside the surface or surfaces perpendicular to the base ofthe complete cone and intersecting it at the outline of the workingarea, the area of the base of the complete cone being large enough tocircumscribe or even extend everywhere beyond the outline of the workingarea. This enables the base of this portion of the explosive to besuperimposed on the plane end of a column of explosive of the requiredshape without overhanging it. Such truncations are without any adverseeffect on the plane detonation wave front characteristics of the charge.An example of a composite explosive charge suitable for working on anon-circular area in accordance with this invention is shown in Figuresand 6, where like numerals as those used in Figures 1 and 2 representlike parts. The composite explosive charge of Figures 5 and 6 forworking on a square area is formed by truncating the cone-shapedexplosive charge 5 so as to form four equal length surfaces l3 at rightangles to each other and normal to the base of the conical explosivecharge 5 The portion of the explosive charge in the form of the planeended column may for instance consist of an 80:20 mixture by weight oftrinitrotoluene and sodium chloride milled to a fine grist.

The explosive constituting the core of the coned portion mayadvantageously have a velocity of detonation not exceeding about 2300metres per second and the explosive constituting the outer thickness avelocity of detonation 6 considerably "higher, e. g. 3060: -metres :persec end. The core explosive-may consist -for lin stance of *DenabyBowder --whioh consists of "a mixture comprising 12% 59% ammoniummtrate, 6% sodium nitrate, 20% sodium onic-- ride, and 3% cellulosicmaterial and theouter thickness explosive may "consist for instance :ofcyclotrimethylene trinitramine. The ini-tiating means at the-apexof thecone maybe a primeradapted to receive a detonator, =an'd may be:included as a permanent part of the charge, :er supplied separately"like the -detonator :itself. "to be "assembled with the rest of thecharge when it is to lie-exploded. r 1

Tt'w'ill be understood thatin'making up the explosive charge a *casing-suitably compartmented by'means-of structures-of l-ight material isdesirably employed, and that the base of the casing will serve-*as=cushioning'material between the explosive and thezsheet ofides'truetiblercompressible material which may, if desired, ihave thelowrelie'f markings penetrating-through the whole of its thickness :in thefashion :of .a :stencil or through only va apart 10f bits zthickness.:Ihe sharpness .:of :the :markings on the :metal ;plate may be modifiedas desired ..by =interposing :fur ther cushioning .r-material:preferably melow :the sheet of destructible compressible; material.-.The sheet of :ldestructible compressible rrnaterialzandfurther:cnshioningsmaterialshonldbe cigar-charactor .=such ithat :-.they:will not :become mermanently :attached. to the metal plate rafter-thedetonation. .7 woodipaper. :c rdboard or the like may the used. -;Asheet :of cushioning material may .;;also :be zinternosedrbetween themetal plate and ithe :anvil rsulqnorting -.it.

.I aclaim: ,Agcomposite rexplesive :charge ,capablesof producing :agplane. detonation gwavie :flQIlt .comprising ;a right angle;.cone+shape,d rexplosive charge arranged :for detonation by 22,thickness of a priming charge of higher velocity of detonation extendingover the whole of said conically curved surface, the apex of saidthickness of charge of higher velocity of detonation being adapted forreceiving detonation initiating means, and the sine of the base angle ofthe right angled cone-shaped explosive charge being equal to thequotient of the velocity of detonation of the charge of relatively lowervelocity divided by the velocity of detonation of the charge ofrelatively higher velocity.

2. A composite explosive charge capable of producing a plane detonationwave front as set forth in claim 1 wherein the base surface of saidcone-shaped explosive charge is arranged for initiating detonation ofone end of an explosive composition in the form of a planeended columnof uniform cross section having its columnar axis perpendicular to itsplane ends, the velocity of detonation of said conical detonating chargebeing not greater than that of the velocity of said explosive of saidplaneended column.

3. A composite explosive charge capable of producing a plane detonationwave front as set forth in claim 1 wherein said composite charge istruncated by at least one surface normal to the base of the cone-shapedexplosive charge.

4. A composite explosive charge capable of producing a, plane detonationwave front comprising a right angle cone-shaped explosive chargearranged for detonation by a thickness of a priming charge of highervelocity of detonation extending over the whole of said conically curvedsurface and further arranged for concial detonating charge being notgreater than that of the velocity of saidexplosive. of said column, andthesine of the base angle of said right angle cone-shaped explosivecharge being equal to the quotient of the velocity of detonation of thecharge of the right angle coneshaped explosive divided by the, velocityof detonation of the priming charge and having the apex of saidthickness of said priming charge adapted for detonating initiatingmeans. 1

5. A composite explosive charge capable of producing a plane detonationwave front as set forth in claim 4 wherein said composite explosivecharge is truncated by at leastone surface normal to the base of thecone.

6. A method of impressing 10w relief mark: ings into a metal .platewhich comprises interposing a sheet of destructible compressiblematerial having predetermined local variations ofthe kind to causecorresponding differences in energy absorption of a detonation directedthrough it between the metal plate to be impressed and a compositeexplosive charge, said composite explosive charge comprising a rightangle cone-shaped charge arranged for detonation by a thickness of apriming charge of higher velocity of detonation extending :overthe wholeof said conically curved surface, the sine of the base angle of saidcone being equal to the quotient of the velocity of detonation of thecharge of relatively lower velocity divided by the velocity ofdetonation of the charge. of relatively higher velocity and having theapex of said thickness of charge of higher velocity of detonationprovided with detonation initiating means, positioning the saidexplosive charge so that the said initiating means 'is' furthermostremoved from said metal-plate, and detonating said initi ating means.

said composite explosive charge is truncated by at least one surfacenormal to the base of the cone. a v f 8. A method as set forth inclaim.6 wherein the composite explosive charge includes as a portionthereof nearest to the sheet of destructible. compressible material aplane-ended explosive column of uniform cross section having itscolumnar axis perpendicular to its plane ends and one end thereofarranged for detonation by the base of said cone-shaped explosivecharge, the velocity of detonation of said cone-shaped explosive chargebeing not more than that of the explosive of said column. v

9. A method as set forth in claim 6 wherein cushioning sheet material isinterposed between the composite explosive charge and the sheet ofdestructible compressible material.

JOHN HENRY COOK;

REFERENCES CITED The followingreferences are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Propelled Hollow Charges, PopularScience, February 1945, pages 66 and 67.

7. A method as set forth in claimG wherem'

6. A METHOD OF IMPRESSING LOW RELIEF MARKINGS INTO A METAL PLATE WHICHCOMPRISES INTERPOSING A SHEET OF DESTRUCTIBLE COMPRESSIBLE MATERIALHAVING PREDETERMINED LOCAL VARIATIONS OF THE KIND OF CAUSE CORRESPONDINGDIFFERENCES IN ENERGY ABSORPTION OF A DETONATION DIRECTED THROUGH ITBETWEEN THE METAL PLATE TO BE IMPRESSED AND A COMPOSUTE EXPLOSIVECHARGE, SAID COMPOSITE EXPLOSIVE CHARGE COMPRISING A RIGHT ANGLECONE-SHAPED CHARGE ARRANGED FOR DETONATION BY A THICKNESS OF A PRIMINGCHARGE OF HIGHER VELOCITY OF DETONATION EXTENDING OVER THE WHOLE OF SAIDCONICALLY CURVED SURFACE, THE SINE OF THE BASE OF SAID CONE BEING EQUALTO THE QUOTIENT OF THE VELOCITY OF DETONATION OF THE